The challenge in imaging faint objects near bright stars is in reducing the starlight and the noise by many orders of magnitude while efficiently transmitting the planet light. Due to scattered starlight, the planets near bright stars could be observed earlier only at large angular separations and with large telescopes. Using a small aperture telescope system for detecting exoplanets at nearly diffraction limit of their separation from the star can have a significant impact on astronomy as well as other imaging and space communication systems. Vector vortex coronagraphs prove to provide such an opportunity. When used with larger aperture telescopes, a vortex coronagraph would allow detecting planets even closer to the stars, hence brighter and in early stages of formation.
In this new generation of smaller, lighter and more affordable coronagraph systems, the star light is rejected with the aid of phase-based transparent “masks” capable of transmitting planetary light at small angular separation from the star. These so-called vortex vector waveplates (VVW) are complex optical components wherein the optical axis orientation is rotating in space in an axially symmetric manner. Liquid crystals (LCs), particularly, LC polymers (LCPs) are the only material systems that allow fabrication of VVWs with continuous rotation of the optical axis orientation at a high spatial frequency required for obtaining a high topological charge and high contrast. LCs are transparent in visible, near IR and even for longer wavelengths and, due to their high optical anisotropy, the half-wave phase retardation condition is achieved in thin material layers (˜1 micrometer).
Thus, there is a need for a technique that would allow fabricating large diameter VVWs with small singularity size, and broadband at different spectral ranges, including visible and infrared. Particularly important is reducing the defect size to subwavelength sizes.